The leachate from in situ uranium leaching processes most always contains some polythionates. Polythionate concentration is particularly high where the gangue materials are rich in sulfides, such as pyrites. The polythionate concentration is also higher in the early stage of leaching operation. When the leachate is passed over the ion exchange resin for uranium recovery, the polythionates are also adsorbed on the resin strongly. The polythionate adsorption is so strong that they cannot be eluted along with the uranium in the normal elution cycle and become a poison to decrease the uranium loading capacity of the resin in the following loading cycles.
Use of H.sub.2 O.sub.2 or strong caustic solution has been suggested for regeneration of polythionate poisoned resins. However, both procedures attack the resin chemically and physically resulting in shortened resin life.
In application Ser. No. 270,303 abandon filed concurrently herewith by Hans-Peter C. Schmiedel and commonly assigned, there is disclosed and claimed a new process for controlling polythionate poisoning of the ion exchange resin. The process involves treating the poisoned resin with a solution of Na.sub.2 SO.sub.3, preferably 0.1 M, which may also contain another non-reacting salt, e.g. NaCl. The reaction may be represented as follows: EQU S.sub.n O.sub.6.sup.= +(n-3)SO.sub.3.sup.= .fwdarw.S.sub.3 O.sub.6.sup.= +(n-3)S.sub.2 O.sub.3.sup.=,
wherein n is typically 4-8, usually 4.
The treated resin is then eluted with acidic or neutral eluant to remove the conversion products, namely, thiosulfate and polythionates with 3 or less sulfur atoms per molecule. The procedure requires interruption of normal operation schedules so that the sulfite treatment can be carried out. It was believed important to avoid contacting sulfite, being a reducing agent, with the uranium complex in order that the uranium at +6 state will not be reduced and precipitated.
The improved process of the Schmiedel application offers a number of important advantages, however, including avoidance of undesirable physical and chemical degradation of the resin as had been associated with previous attempts to reduce polythionate poisoning. The entire disclosure of that application is incorporated herein by reference.